1. Field of the Invention
This invention is directed to a method of contraception that provides for the reduction or elimination of estrogen in the initial phase of a multiphasic estrogenic/progestogenic contraceptive regimen without compromising contraceptive efficacy or cycle control. The invention is also directed to a multiphase contraceptive kit that may be used to practice the method of the invention.
2. Related Background Art
Contraceptive compositions containing both estrogenic and progestogenic compounds are well known. The progestogenic component of the composition is primarily responsible for the contraceptive efficacy of the composition, while the estrogenic component is employed to reduce undesired side effects, such as breakthrough bleeding or spotting.
The earliest of these estrogenic/progestogenic contraceptive compositions contained a relatively high level of estrogenic component. A constant goal, however, has been to reduce the estrogenic potency of such compositions without reducing contraceptive efficacy and increasing undesired side effects. As described in U.S. Pat. No. 5,888,543, in an attempt to achieve this goal, numerous regimens have been developed in which the progestin/estrogen combination is administered in a monophasic regimen (fixed dose) or as biphasic or triphasic regimens (varied dose).
A particularly advantageous technique for reducing total estrogenic administration is described in U.S. Pat. No. 4,962,098. This describes a triphasic method of contraception using a progestogen/estrogen combination in which the amount of estrogen is increased stepwise over the three phases. The first phase is 4-7 days, the second phase is 5-8 days and the third phase is 7-12 days. Preferably, the administration of the contraceptive compositions for the three phases will be 21 days followed by a 7 day placebo period. For all three phases the progesten is 0.5 to 1.5 mg of norethindrone acetate, while about 10 to 30 mcg of ethinyl estradiol is used in the first phase, about 20 to 40 mcg of ethinyl estradiol is used in the second phase and 30 to 50 mcg of ethinyl estradiol is employed in the third phase.
There is a continuing desire, however, to further reduce the amount of estrogenic component in an estrogenic/progestogenic composition with continued contraceptive efficacy while avoiding undesired side effects. Heretofore it was believed that at least 10 mcg of ethinyl estradiol or its estrogenic equivalent was needed in an estrogenic/progestogenic composition to assure contraceptive efficacy. It has now been surprisingly discovered that the amount of estrogenic component in the first phase of a triphasic regimen can be significantly reduced or eliminated without compromising efficacy or cycle control.